HDU 2196 Computer(树的直径)

#include <iostream>
#include <cstdio>
#include <cstring>
#include <queue>
#define ll long long
#define maxn 20005
#define inf 0x3f3f3f3f
using namespace std;
struct Node{
  int to,next,w;
}Edge[maxn];
int head[maxn],num;
int dist[maxn], pre[maxn];
bool vis[maxn];
int T,n,m;

void init(){
  for(int i=0;i<=n;i++){
    head[i] = -1;
  }
  num = 0;
}

void add(int u,int v,int w){
  Edge[num].to = v;
  Edge[num].w = w;
  Edge[num].next = head[u];
  head[u] = num ++;
}

void bfs(int x){
  queue<int> q;
  memset(dist,0,sizeof(dist));
  memset(vis,false,sizeof(vis));
  q.push(x);
  while(!q.empty()){
    int u = q.front();
    q.pop();
    vis[u] = true;
    for(int i=head[u];i!=-1;i=Edge[i].next){
      int to = Edge[i].to;
      if(vis[to] == false){
        vis[to] = true;
        dist[to] = dist[u] + Edge[i].w;
        q.push(to);
      }
    }
  }
}

int main()
{
  while(~scanf("%d",&n)){
    init();
    for(int i=2;i<=n;i++){
      int v, w;
      scanf("%d%d",&v,&w);
      add(i, v, w);
      add(v, i, w);
    }
    bfs(1);
    int Max = 0;
    int pos = 0;
    for(int i=1;i<=n;i++){
      if(Max < dist[i]){
        Max = dist[i];
        pos = i;
      }
    }
    bfs(pos);
    Max = 0;
    for(int i=1;i<=n;i++){
      if(Max < dist[i]){
        Max = dist[i];
        pos = i;
      }
      pre[i] = dist[i];
    }
    bfs(pos);
    for(int i=1;i<=n;i++){
      printf("%d\n", max(pre[i], dist[i]));
    }
  }
  return 0;
}